1. Technical Field
The present invention relates to a method of removing metals from hydrocarbon oil.
2. Description of the Related Art
With the recent excavation of new oil wells, crude oil native to West Africa, including Chad, Sudan, etc. (Doba, Kuito), crude oil native to the North Sea (Heidrun, Captain), crude oil native to China (Bobai, Shangri), crude oil native to Indonesia (Shering), and crude oil native to North America (San Joaquin Valley) are being produced. However, such crude oil has low quality, and may suffer from pollution of heat exchangers upon use thereof, difficulty in treating discharged materials, poisoning of catalysts due to specific metal salts, and other problems. Hence, in order to increase the competitiveness of the above crude oil, additional processing for treating metals that act as pollutants is required.
Among metals, calcium is mainly present in the form of calcium naphthenate in crude oil, and causes very serious problems. The problems with high-calcium crude oil are as follows: the separation of a water layer becomes problematic during a desalting process because calcium naphthenate functions as an emulsion stabilizer, whereby an excess of water is fed into a refining unit, or an excess of organic material is fed into a wastewater disposal unit, undesirably lowering the overall processing efficiency of crude oil. Furthermore, calcium remaining in the oil residue of the crude oil passed through the refining unit may deactivate the catalyst within a very short time during the catalytic cracking process using a fluid catalytic cracking unit (FCCU) or a residue fluidized catalytic cracking unit (RFCCU). Furthermore, when residue is combusted in a boiler, a large amount of calcium sulfate is produced in the boiler, undesirably drastically lowering the boiler efficiency. Hence, high-calcium crude oil needs an additional calcium treatment process before a typical refining process, and the demand for methods of efficiently removing calcium that are able to ensure economic benefits compared to when using general crude oil is increasing.
The emulsion mixture of the desalting process is guided into a desalting device including plates that are electrically charged and disposed parallel to each other. Under such an array, an oil and water emulsion is exposed to an electric field applied thereto. In the water droplets in the emulsion, induced dipoles are formed, thus causing electrostatic attractive force between water droplets to thereby lead to combined water droplets having a larger size. Consequently, the emulsion is separated into two phases, that is, an oil phase (an upper layer) and a water phase (a lower layer). The streams of desalted crude oil and effluent water are discharged from the desalting device.
U.S. Pat. No. 4,778,589 discloses a method of rising hydroxo-carboxylic acid, especially citric acid in an aqueous solution form, in order to remove calcium from a hydrocarbon oil fraction. When calcium is removed, calcium citrate is produced. Calcium citrate has low solubility in water and thus causes a large amount of precipitates to remain in the desalting unit, thus drastically lowering the calcium removal efficiency. Furthermore, since the aqueous solution is used, the pH of the aqueous solution is excessively increased upon the removal of calcium from a high-concentration hydrocarbon oil traction, undesirably causing corrosion of the processing unit.
U.S. Pat. No. 4,778,590 discloses a method of removing calcium using aminocarboxylic acid or salts thereof, especially EDTA (Ethylene Diamine Tetra Acetic, acid). However, EDTA, having low solubility in water, has to be provided in the form of a calcium scavenger aqueous solution using an excess of water, and is difficult to transport and is not easy to use, undesirably incurring economic and industrial defects.
The aforementioned patents adopt the manner in which an inorganic acid or an organic acid, especially a monoacid, diacid, or hydroxyl acid, is first dissolved in water to prepare a calcium scavenger concentrate, which is then diluted with a large amount of water in the desalting process, in order to remove calcium from the hydrocarbon oil fraction including crude oil.
Such a manner is used to increase the calcium removal efficiency by mixing, within a short time, the lipophilic layer corresponding to the hydrocarbon oil fraction with the water layer in which the calcium scavenger is dissolved, and the reaction is caused at the interface of two layers, which are not miscible. In the case where crude oil having a high calcium concentration is used, mixing is limited due to the viscosity, making it difficult to use a high-concentration mixing ratio.
In consideration thereof, there is a need to develop novel methods of effectively removing metal pollutants, especially calcium, from the feed including hydrocarbon oil However, metal pollutants in the crude oil are not limited to calcium, and thus embodiments of the present invention are intended to provide a method of effectively removing calcium from crude oil and additionally removing other metal pollutants, especially iron, other than calcium.